Grooved staved bearing assembly

ABSTRACT

A bearing assembly for supporting a drive shaft of a ship wherein the shaft is generally to be supported by such bearing assembly in a horizontally extending position. The bearing assembly has a housing with a cylindrical shell mounted therein having a central bore with a longitudinally extending central axis. The shell has a plurality of circumferentially spaced staves provided therein which project into the central bore to support the drive shaft. The staves have transverse grooves provided therein.

BACKGROUND OF THE INVENTION

[0001] This invention relates to a bearing assembly and moreparticularly to a new and novel bearing assembly for use in supporting awater lubricated propeller shaft as in large naval ships. Bearingassemblies with elastomeric bearing elements are particularly suited forthis purpose because of their excellent ability to withstand the effectsof corrosive fluids and to abrasion resulting from particles of foreignmatter carried in suspension in the sea water in which the shaft andbearing assembly operates. Such bearing assemblies with theirelastomeric bearing elements have been made and are still being madewith outer non-corrosive support or shell with a plurality ofcircumferentially evenly spaced elastomeric staves therein.

SUMMARY OF THE INVENTION

[0002] The present invention is directed to a novel bearing assemblyutilizing an outer shell and a plurality of circumferentially spacedbearing elements in contact with the shaft, the bearing elements havingtransverse grooves or a hydrodynamic pattern provided therein to therebyreduce the bearing friction torque thus enhancing the performance of thebearing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0003]FIG. 1 is a cross sectional view of a bearing assembly inaccordance with the present invention.

[0004]FIG. 2 is an isometric view of a bearing stave in accordance withthe present invention.

[0005]FIGS. 3a-3 b are isometric views of alternate embodiments forbearing material for use in a bearing assembly in accordance with thepresent invention.

[0006]FIG. 4 is a cross sectional view of a second embodiment of abearing assembly in accordance with the present invention.

DETAILED DESCRIPTION

[0007] Referring now to FIG. 1, wherein a bearing assembly 210 inaccordance with the present invention includes a housing 215 havingthree staves 240 provided around the radial inner portion thereof. Eachstave 240 is held in place by a pair of elastomeric members 260. A rigidplate or bar 264 is disposed on top of each elastomeric member 260. Ascrew or bolt 266 extends through a clearance shaft (not shown) in eachbar 264 and elastomeric member 260 and engages with threaded hole 267 inhousing 215. Tightening screw 266 pulls rigid plate 264 toward housing215, thereby compressing and deforming each elastomeric member 260 toexpand sideways and put compression on each stave 240 and hold them inplace.

[0008] Each stave 240 has a grooved bearing surface 241, a substantiallyflat back side 282 and is supported by one or more shims or pads 284,286. Preferably, each stave 240 backside 282 is in contact with a topshim 284 comprised of a hard material, (such as metal, compositematerial or other hard plastic), which is supported by a bottom pad 286comprised of a resilient or compressible material, (such as softplastic, rubber or other elastomer). Flat backed staves are moreeconomical to produce compared with round backed staves. Lower stave 240supports drive shaft 223, and the two upper staves 240 tangentiallyengage the drive shaft 223 in cooperative action with the lower stave240 to prevent extraneous flexing of the shaft 223.

[0009] Housing 215 is preferably made from a metallic structure such asbrass, a plastic shell or a composite non-metallic structure. Housing215 is most preferably comprised of fiberglass reinforced epoxy, with aglass content on the order of 70% by weight.

[0010] Staves 240 are preferably made from an elastomeric/plasticcomposite, such as that described in commonly owned U.S. Pat. No.3,993,371 or a homogeneous slippery polymer alloy (SPA) such as isdisclosed in U.S. Pat. Nos. 4,725,151 and 4,735,982, all of which arehereby fully incorporated herein by reference. SPA is a thermoplasticand a thermoset rubber compound, along with a smaller amount of alubricant. SPA is a heterogeneous composition wherein the thermoplasticexists in a continuous phase and the thermoset is dispersed therein as adiscontinuous phase. In other words a thermoplastic matrix is formed,having the thermoset compound and the lubricant dispersed therein, asopposed to an admixture.

[0011] The thermoplastic compound can be any polymer which exhibitstough, low friction and good wear resistant properties. A specific groupof such polymers are the various ultra high molecular weightpolyethylenes (UHMWPE) which are known to the art as well as to theliterature. Ultra high molecular weight polyethylene are generallyclassified as those having a weight average molecular weight of greaterthan 2.5 million, that is from about 3.0 million to about 7.0 millionusing the solution viscosity method. A desired range is from about 4million to about 6.5 million with a preferred range being from about 5million to about 6 million. Such polyethylene are commercially availablefrom Hoechst Celanese Corporation under the name GUR 413.

[0012] The ultra high molecular weight polyethylene as well as otherpolymers generally suitable for use in the present invention typicallyhave low friction properties such as a breakaway coefficient of staticfriction at 0 rpm of 0.25 or less, desirably 0.20 or less and preferably0.15 or less. The desired thermoplastic material of the presentinvention also have a toughness as measured by a Izod notch impact test(ASTM D256) of 20 or greater and preferably of 30 or greater. However,unnotched test samples did not fail. The thermoplastic material of thepresent invention also have good wear resistance as measured by a sandslurry abrasion test. The sand slurry abrasion test is a test of HoechstCelanese Corporation wherein generally a test specimen (1″×3″×¼″) isrotated at 1200 RPM over a 24 hour period in a slurry containing 2 partsof water and 3 parts of sand.

[0013] An effective amount of the ultra high molecular polyethylene isutilized such that it forms a continuous phase in the SPA. Generally,the amount of a thermoplastic compound is sufficient to coat thethermoset rubber compound which generally exist in the form of particlesand more desirably an amount in excess of that required to coat therubber particles. Based upon the total weight of the SPA, the amount ofthe thermoplastic often utilized is from about 25% to about 90% byweight, desirably from about 40% to about 75% by weight and preferablyfrom about 55% to about 65% by weight.

[0014] The thermoset compound is a cured rubber compound which typicallyhas low friction as well as good oil and water resistant properties. By“low friction” it is meant that rubber bearings of a desired thicknessrange, when water lubricated, develop hydrodynamic lubrication at normaljournal (shaft) operating speeds. Thin rubber bearings develophydrodynamic friction at lower shaft speeds than any other known bearingmaterial due to the Plasto-Elastohydrodynamic effect. Hydrodynamiclubrication is the developing of a fluid film between the bearing and arotating shaft. By the terms “oil and water resistant”, it is meant thatthe elastomer is unaffected (not dissolved or softened) and the volumeincrease caused by swell in water is under 5%, and preferably under 3%.

[0015] Generally any rubber compound having such friction and waterresistant properties can be utilized. A specific group of such compoundsare various nitrile rubbers which are known to the art and to theliterature. For example, the various Hycar nitrile rubber compoundsmanufactured by the BFGoodrich Company can be utilized. The variousharder nitrile rubber compounds are generally preferred. A specificexample of such-a rubber is compound H-201 (85+/−5 Shore A hardness)manufactured by the BFGoodrich Company. Another example is a softernitrile rubber such as compound H-203, also manufactured by theBFGoodrich Company which has a Shore A hardness of about 65±5. Otherrubbers include Butyl rubber, EPDM, that is rubber made fromethylene-propylene-diene monomers, and fluorelastomers based on thecopolymer of vinylidene fluoride and hexafluoropropylene thought to havethe following repeating structure —CF—CH—CF—CF(CF)—. Such copolymers aresold under the Trademark “Viton” by DuPont. Although these other rubbercompounds can be utilized, the nitrile rubbers are highly preferred.

[0016] It is an important aspect of the present invention that therubber compound can be initially dry blended or mixed with thethermoplastic compound before the alloy is formed.

[0017] Accordingly, the rubber compound is cured and in order to mix thetwo components, it is ground to a suitable size. Conventional grindingmethods can be utilized such as mechanical or cryogenic grinding.Particle size of the cured rubber compound is generally important. Theparticle size is generally measured as being finer, that is being ableto pass through, a specific Tyler mesh screen. The cured rubbercompounds thus generally have a particle size smaller than 35 mesh,desirably smaller than 65 mesh, and preferably smaller than 100 mesh.The amount of the cured rubber in the SPA is generally from about 10% toabout 70% by weight, desirably from about 12% to about 40% by weight andpreferably from about 15% to about 30% by weight based upon the totalweight of the SPA.

[0018] The lubricant is generally added in the form of a solid and henceis non-liquid. In order to ensure a good dispersal thereof, thelubricant typically is in the form of a powder. By the term powder, itis meant that a majority, and at least 70%, 80% or 90% and moredesirably at least 95% of the particles are smaller than a Tyler 100mesh screen, that is 150 microns. Desirably, a majority of the powder,typically 80%, 90%, or even 95% is smaller than 200 mesh, that is 75microns. Preferably a majority of the graphite powder, that is 70%, 80%,or 90% is smaller than 325 meshes, that is 44 microns. Any lubricantknown to the art as well as to the literature can be utilized whichimparts lubricating properties to the SPA. By lubricating properties itis meant that the coefficient of friction of the surface of the formedSPA is reduced, as for example, on the order of at least 10% and moredesirably at least 20% or 30% when wear starts. The lubricant alsoshould be nonabrasive. Graphite constitutes a preferred lubricant. Anexample of a specific graphite is grade 117-A, manufactured by AsburyGraphite Mills, Inc. Another specific lubricant is molybdenum disulfide.Although not generally preferred, molybdenum disulfide is desirable indry end use applications where moisture is not available, even asatmospheric moisture vapor. Silicone oils can also be utilized in anamount of from about 2% to about 10% by weight and desirably from about3% to about 6% by weight based upon the total weight of the SPA.Examples of specific silicone oils include 200 Fluid manufactured by DowCorning.

[0019] The amount of the lubricant generally is from about 0.5% or 3% byweight to about 25% by weight, desirably from about 1.0% to about 20% byweight, and preferably from about 2% to about 10% by weight based uponthe total weight of the SPA.

[0020] To this end, it has been discovered that certain material factorsfor staves 240 are important. First, hydrophobic materials arepreferred. Second, the elastomer hardness should be about 70 shore A.Third, the ratio of journal diameter of the shaft to the top width ofthe stave should be about 4 to 7. Fourth, the elastomer thickness shouldbe about 0.125 inch to 0.312 inch. Fifth, the surface finish of thestave should be under 10 micro inches. Sixth, harder polymer alloybearing contact material, such as the SPA material described aboveprovides preferable wear and friction characteristics.

[0021] Elastomeric members 260 are preferably comprised of natural ornitrile rubber compounds, and are preferably 0.75 to 1.5 inches widebefore compression. Rigid plates 264 are preferably comprised of ametal, such as stainless steel, or a hard plastic, such as fiberreinforced epoxy. The compressed elastomeric members 260 expand to gripthe sides of the staves 240. They also distort around the ends of thestaves to provide an axial locking feature.

[0022] Bottom pads 286 offer alignment capability. Top shim 284 isutilized to control the operating clearance between the bearing bore andthe shaft 223 to eliminate the grinding of critical stave surface and tosimplify the bearing renewal and replacement process. Each stave in astave type bearing functions as an individual and independent bearingsurface. The deflection capability of bearing 210 provides for a zeroclearance bearing (ZCB). ZCB's are more stable because, among otherthings, the unloaded staves can be depressed by the rotating shaft 223as it develops hydrodynamically pressurized lift-off pressure on theload carrying staves. Furthermore, gritty water stave wear in a ZCB willbe greatly reduced because the reverse flow particle rejection processis most efficient when the shaft (journal) is in contact with all of thestaves (no unloaded clearance space). In a ZCB there is zero clearancebetween all of the staves and the shaft. In a conventional stave bearingdesigned with initial clearance, the side or top staves are unloadedwith the shaft not touching them. The efficiency of the reverse flowparticle rejection process is reduced with any clearance present,thereby causing wear of surfaces of the side or top staves. The gritparticles pass through the clearance space instead of being rejectedback, thereby flowing out through the water grooves.

[0023] The three staves are preferably located approximately 120° apart(angle A), with the two upper staves located approximately 30° (angle B)above horizontal line 280 and the lower stave located approximately 90°below horizontal 280.

[0024] Referring now to FIG. 2, wherein a stave 240 for the bearing 210of FIG. 1 is illustrated. Staves 240 have a plurality of transversegrooves 290 provided therein and distributed along the axial length ofthe stave thereby leaving a plurality of lands or protrusions 241protruding towards the axial centerline. The grooves may be eithermolded into the material or machined into the material, with machiningthe preferred method. The particular dimensions for the staves willdiffer for each application. For a stave on the order of 0.75 inchesthick, the grooves 290 are preferably on the order of 0.25 inches deepand 0.33 inches wide, with a separation between grooves of on the orderof 1 inch. Machining grooves in the staves increases the amount ofcontact pressure in between grooves. The stave dimensions and groovedimensions must be picked such that the applied load is high enough forlow friction and wear to occur, but the bulge ratio must be also lowenough for the staves to adjust and form a lubricant trapping pocket.

[0025] Referring now to FIGS. 3a-3 b, wherein alternate embodiments forstaves 240 is illustrated. The bearing material is molded in largeflexible slabs. The material is molded and shaped against a plate orrough fabric with many protuberances lands, or contact points, 414, 424wherein the protuberances can each individually become hydrodynamicbearing surfaces when fluid lubricated. The material is molded andshaped against a rough fabric (FIG. 3a) or plate with manyprotuberances. The molded staves consist of an elastomeric/plasticcomposite, such as that described in commonly owned U.S. Pat. No.3,993,371 or most preferably a homogeneous slippery polymer alloy (SPA)such as is disclosed in U.S. Pat. No. 4,725,151 and 4,735,982, all ofwhich are hereby fully incorporated herein by reference. The SPA bearingmaterial layer is preferably on the order of 0.125 inches thick. It isthen adhered during slab cure to a nitrile rubber backing sheet. Therubber backing makes the slab flexible, and when abraded, is easy tobond to the metal or composite bearing housing using room temperaturecuring epoxy adhesives or contact cement. The rubber backing is rapidlyand easily sanded or ground by means of a machine to give the correctoverall slab thickness for the particular bearing size. The adhesivelayer adds around 0.001 inches to the bearing total wall thickness.There is therefore no need to grind or machine the bearing surface.Grinding the bearing surface increases friction and wear. The full stavethickness is preferably 0.625 inches to 1.1 inches.

[0026] It is to be noted that the staves in FIGS. 3a-3 b may be madecompletely from the aforementioned SPA material. That is, the staves 240may not have a bottom layer 410 and therefore would be comprisef of asingle layer comprised of the material for layer 412.

[0027] Referring now to FIG. 3a, an alternate stave material 240 may bemanufactured by providing a patterned bottom layer 410 of elastomer in amold. The preferred elastomer is catalog number H-201 available from theB.F.Goodrich Company. Next, a top layer 412 of slippery polymer alloy(SPA) is provided on the elastomer. A thermoplastic and a thermosetrubber compound, along with a smaller amount of a lubricant form theSPA. The SPA is a heterogeneous composition wherein the thermoplasticexists in a continuous phase and the thermoset is dispersed therein as adiscontinuous phase. In other words a thermoplastic matrix is formed,having the thermoset compound and the lubricant dispersed therein, asopposed to an admixture.

[0028] The thermoplastic compound can be any polymer which exhibitstough, low friction and good wear resistant properties. A specific groupof such polymers are the various ultra high molecular weightpolyethylenes (UHMWPE) which are known to the art as well as to theliterature. Ultra high molecular weight polyethylene are generallyclassified as those having a weight average molecular weight of greaterthan 2.5 million, that is from about 3.0 million to about 7.0 millionusing the solution viscosity method. A desired range is from about 4million to about 6.5 million with a preferred range being from about 5million to about 6 million. Such polyethylene are commercially availablefrom Hoechst Celanese Corporation under the name GUR 413.

[0029] The ultra high molecular weight polyethylene as well as otherpolymers generally suitable for use in the present invention typicallyhave low friction properties such as a breakaway coefficient of staticfriction at 0 rpm shaft speed of 0.25 or less, desirably 0.20 or lessand preferably 0.15 or less. The desired thermoplastic material of thepresent invention also have a toughness as measured by a Izod notchimpact test (ASTM D256) of 20 or greater and preferably of 30 orgreater. However, unnotched test samples did not fail. The thermoplasticmaterial of the present invention also have good wear resistance asmeasured by a sand slurry abrasion test. The sand slurry abrasion testis a test of Hoechst Celanese Corporation wherein generally a testspecimen (1″×3″×¼″) is rotated at 1200 RPM over a 24 hour period in aslurry containing 2 parts of water and 3 parts of sand.

[0030] An effective amount of the ultra high molecular polyethylene isutilized such that it forms a continuous phase in the SPA. Generally,the amount of a thermoplastic compound is sufficient to coat thethermoset rubber compound which generally exist in the form of particlesand more desirably an amount in excess of that required to coat therubber particles. Based upon the total weight of the SPA, the amount ofthe thermoplastic often utilized is from about 25% to about 90% byweight, desirably from about 40% to about 75% by weight and preferablyfrom about 55% to about 65% by weight.

[0031] The thermoset compound is a cured rubber compound which typicallyhas low friction as well as good oil and water resistant properties. By“low friction” it is meant that rubber bearings of a desired thicknessrange, when water lubricated, develop hydrodynamic lubrication at normaljournal (shaft) operating speeds. Thin rubber bearings develophydrodynamic friction at lower shaft speeds than any other known bearingmaterial due to the Plasto-Elastohydrodynamic effect. Hydrodynamiclubrication is the developing of a fluid film between the bearing and arotating shaft. By the terms “oil and water resistant”, it is meant thatthe elastomer is unaffected (not dissolved or softened) and the volumeincrease caused by swell in water is under 5%, and preferably under 3%.

[0032] Generally any rubber compound having such friction and waterresistant properties can be utilized. A specific group of such compoundsare various nitrile rubber compounds which are known to the art and tothe literature. For example, the various nitrile rubber compoundsmanufactured by the BFGoodrich Company can be utilized. The variousharder nitrile rubber compounds are generally preferred. A specificexample of such a rubber is compound H-201 (85±5 Shore A hardness)manufactured by the BFGoodrich Company. Another example is a softernitrile rubber such as compound H-203, also manufactured by theBFGoodrich Company which has a Shore A hardness of about 65±5. Otherrubbers include Butyl rubber, EPDM, that is rubber made fromethylene-propylene-diene monomers, and fluorelastomers based on thecopolymer of vinylidene fluoride and hexafluoropropylene thought to havethe following repeating structure —CF—CH—CF—CF(CF)—. Such copolymers aresold under the Trademark “Viton” by DuPont. Although these other rubbercompounds can be utilized, the nitrile rubbers are highly preferred.

[0033] It is an important aspect of the present invention that the curedrubber compound can be initially easily dry blended or mixed with thethermoplastic compound before the alloy is formed.

[0034] Accordingly, the rubber compound is cured and in order to mix thetwo components, it is ground to a suitable size. Conventional grindingmethods can be utilized such as mechanical or cryogenic grinding.Particle size of the cured rubber compound is generally important. Theparticle size is generally measured as being finer, that is being ableto pass through, a specific Tyler mesh screen. The cured rubbercompounds thus generally have a particle size smaller than 35 mesh,desirably smaller than 65 mesh, and preferably smaller than 100 mesh.The amount of the cured rubber in the SPA is generally from about 10% toabout 70% by weight, desirably from about 12% to about 40% by weight andpreferably from about 15% to about 30% by weight based upon the totalweight of the SPA.

[0035] The lubricant is generally added in the form of a solid and henceis non-liquid. In order to ensure a good dispersal thereof, thelubricant typically is in the form of a powder. By the term powder, itis meant that a majority, and at least 70%, 80% or 90% and moredesirably at least 95% of the particles are smaller than a Tyler 100mesh screen, that is 150 microns. Desirably, a majority of the powder,typically 80%, 90%, or even 95% is smaller than 200 mesh, that is 75microns. Preferably a majority of the graphite powder, that is 70%, 80%,or 90% is smaller than 325 meshes, that is 44 microns. Any lubricantknown to the art as well as to the literature can be utilized whichimparts lubricating properties to the SPA. By lubricating properties itis meant that the coefficient of friction of the surface of the formedSPA is reduced, as for example, on the order of at least 10% and moredesirably at least 20% or 30% when wear starts. The lubricant alsoshould be nonabrasive. Graphite constitutes a preferred lubricant. Anexample of a specific graphite is grade 117-A, manufactured by AsburyGraphite Mills, Inc. Another specific lubricant is molybdenum disulfide.Although not generally preferred, molybdenum disulfide is desirable indry end use applications where moisture is not available, even asatmospheric moisture vapor. Silicone oils can also be utilized in anamount of from about 2% to about 10% by weight and desirably from about3% to about 6% by weight based upon the total weight of the SPA.Examples of specific silicone oils include 200 Fluid manufactured by DowCorning.

[0036] The amount of the lubricant generally is from about 0.5% or 3% byweight to about 25% by weight, desirably from about 1.0% to about 20% byweight, and preferably from about 2% to about 10% by weight based uponthe total weight of the SPA.

[0037] Next, a pattern is transferred into the top layer of the bearingsurface of bearing material 22. The preferred method of transferringthis pattern is to place a polyester sheet between a piece of heavy,loose knit or loose weave fabric which presses the polyester sheet andfabric into the surface of SPA bearing material 22 before melting andmolding takes place. The fabric is preferably catalog no. 8708 availablefrom Georgia Duck The polyester release sheet is preferably 0.003 inchthick Mylar. The polyester sheet smooths out the resultant SPA layer androunds the edges so the protuberances, lands, or contact points 414 caneach individually become hydrodynamic bearing surfaces when fluidlubricated. It is to be noted that prior to pressing the polyester andfabric into the material, the fabric should be sprayed with a moldrelease, such as catalog no. RTC 9110, manufactured by Chem-Trend, in amanner well known in the art to ensure the fabric can be removed aftercuring. After the fabric and polyester sheet have been placed on top ofthe uncured bearing section it should be pressed in,, such as by closingthe mold. The material is then cured for approximately 4.5 hrs. underpressure of approximately 1000 to 1500 psi at approximately 350° F.After this curing process, the temperature of the mold is allowed toreturn to ambient while the pressure is maintained. The mold should beallowed to cool down for approximately 1 hr. after curing. It has beenfound that cooling the composite under pressure helps to prevent warpingof the final article. Application of water to the outside of mold mayalso be utilized to reduce the mold cooling time to 1 hour to preventwarping of the finished product.

[0038] Referring now to FIG. 3b, an alternate bearing material may bemanufactured in accordance with the procedure for the compositeillustrated in FIG. 3a, thereby yielding a composite having a bottomlayer 420 of elastomer and a top layer 422 of SPA having diamond shapedprotuberances, lands, or contact points 424 provided therein. Theprotuberances 424 protrude axially inward and can each individuallybecome hydrodynamic bearing surfaces when fluid lubricated. The diamondshaped pattern in the top layer 422, however, is provided by utilizing arubber mold having the appropriate impression or pattern providedtherein. A polyester sheet, such as Mylar, may be placed between therubber mold and the SPA before curing. The polyester sheet is preferablyon the order of 0.003 inches thick. The polyester sheet smooths out theresultant SPA layer and rounds the corners of the protuberances.

[0039] It is to be noted that other shape and size patterns notspecifically disclosed herein maybe provided in the top alloy layer inorder for the bearing to be hydrodynamic.

[0040] Referring now to FIG. 4, wherein a bearing assembly 310 inaccordance with an alternate embodiment of the present invention isgenerally similar to the bearing assemblies illustrated hereinbefore inthe previous figures and is thus indicated by reference numeralscorresponding to those discussed above, except that a 300 “prefix” isutilized.

[0041] A housing 315 has three staves or lands 340 provided around theradial inner portion thereof. Staves 340 are formed as a unitary orintegral inner housing or lining 390, which is preferably made from theSPA elastomeric/plastic composite described hereinbefore. Housing 315 ispreferably made from the housing materials also described hereinbefore.Lining 390 is preferably manufactured in the manner described in U.S.Pat. No. 4,735,982 referenced hereinbefore, and installed in the housing315 while it is still hot from the transfer molding process. Lining 390is attached to the housing preferably utilizing an adhesion promoter andcross-linking agent, such as Vanchem HM-50 available from R.T.VanderbiltCo. The prime advantage of this adhesive over others is it's hotstrength. Other attachment means, however, may be utilized to secure thelining into the housing.

[0042] The length to diameter ratio (L/D) of prior elastomer landedstave type bearings is required to be on the order of four to one forwear and life reasons. Bearing 310 permits much lower L/D, possibly onthe order of two to one or even one to one, thereby reducingmanufacturing costs. Also, lining 390 is relatively simple tomanufacture and alleviates the need for machine finishing of the bore ofhousing 315. The bearing surface 341 of each land 340 has either groovesor a pattern provided therein in accordance with the staves shown anddescribed hereinbefore in FIGS. 2 and 3a-3 c.

[0043] It will be apparent that, although a specific embodiment and acertain modification of the invention has been described in detail, theinvention is not limited to the specifically illustrated and describedconstructions since variations may be made without departing from theprinciples of the invention.

1. A bearing assembly for holding a shaft comprising: an outer shellhaving a central opening with a central axis and an inner surfacedefined by said central opening; and, a plurality of staves disposed onsaid inner surface for contacting and supporting the shaft, said staveshaving transverse grooves provided therein.